Estimation of landing impulse absorbing ability by ground reaction force

Abstract

The purpose of this study was to estimate the landing impulse absorbing ability for the peak force time and the resultant force from the viewpoint of the skill for dispersion of impulse. This study consisted of two experiments: Comparison between landing impulse absorbing ability and different lengths of landing distances, and comparison of landing impulse absorbing ability between two groups of different motor ability levels (n=8 per group) which were selected by a self-estimate questionnaire which included 37 items concerning gross motor ability. For example, "Can you ride a bicycle?", "Can you walk on stilts?", "Can you serve a ping-pong ball with back handed service?". A three dimensional force plate was used. Upward , forward and backward ground reaction force curves were obtained for falls from a 60cm tall bench. The results were as follows: 1. Comparison between the good and the poor groups. 1) The resultant force of the poor group was three times larger than that of the good groups. 2) A significant difference in the angle of the resultant force was found; that is, while the good group showed a gradual change, the boor group showed an abrupt change from 0.4 to 0.6 sec after the landing moment. 3) The upward impulses were compared between the two groups but no significant difference was found each other. 2. Comparison between various lengths of the landing distances. 1) No significant corre1ation was obtained between the peak force times and the landing distances. 2) A maximum resultant force was found to be 0.2sec from the landing moment when the landing distances were 30 and 60 cm. In the case of a 90 cm landing distance, a maximum resultant vector was found to be from 0.3 found to be 0.4sec after the landing moment. 3) The 1onger the landing distance, the greater the decrease in the coefficient of variance of the resultant force. These results indicated that the subjects who were superior in landing ability had a so called "smoothing ability" which was based on the function of the dispersion of landing impulse in a unit of time. Previous reports have indicated that the peak force time and the ratio of peak force to weight were used to estimate the landing impulse absorbing ability. The findings suggest that the resultant force should also be added to the parameters for the estimation of the landing impulse absorbing ability.